1. Field of the Invention
The present invention relates to binoculars having diopter adjustment. More particularly, the present invention relates to binoculars in which a mechanism for a diopter adjustment is simply constructed with high operability in addition to a mechanism for focus adjustment.
2. Description Related to the Prior Art
Binoculars as an optical instrument include right and left side optical systems for eyes of a user to view a scene. Each of the right and left side optical systems includes objective lens optics and ocular lens optics. Various methods of adjusting the focusing of the binoculars are known in the optical field. For example, the individual focusing (IF) method is known in which a focus adjusting ring is associated with each of the right and left side optical systems, and is rotated for focus adjustment of the right and left side optical systems in a discrete manner. Also, the central focusing (CF) method is known in which a single focus adjusting ring is used commonly for the right and left side optical systems, and is rotated for focusing of the right and left side optical systems simultaneously in a linked manner. In any of the focus adjusting methods, a focus lens/lens group included in each of the right and left side optical systems is moved on an optical axis for the purpose of focusing.
If a user has a difference in sight between his or her eyes, it is necessary in the right and left side optical systems to focus an image at both of the eyes. It is possible in the IF method of the binoculars to adjust the right and left side optical systems suitably in view of the difference in sight, because of the separate focusing. However, the binoculars of the CF method is provided with a diopter adjusting ring according to requirement in addition to the focus adjusting ring which adjusts focusing of the right and left side optical systems simultaneously. The diopter adjusting ring moves a first optical system of the right and left side optical systems on the optical axis in an independent manner from a second optical system. At first in the operation, the focus adjusting ring in the binoculars of the CF method is rotated to focus the first optical system. Then the diopter adjusting ring is operated to adjust the second optical system for focusing in an equal manner.
U.S. Pat. No. 5,064,279 (corresponding to JP-A 3-163512) and JP-A 2000-056205 disclose examples in which the diopter adjusting ring is disposed about one of eye cups on the right side, or disposed together with the focus adjusting ring in a coaxial manner with a bridge or hinge mechanism between lens barrels of the right and left side optical systems. In the first type of those, one of the eye cups is shifted by operation of the diopter adjusting ring to move the ocular lens optics back or forth. However, there is a shortcoming in that a difference occurs between protruding amounts of the eye cups owing to the shift.
In the binoculars of the CF method, the focus adjusting ring and the diopter adjusting ring separate from the focus adjusting ring are disposed in association with the right and left side optical systems. Rotational operation for those is not simple, so that operability in the adjustment is somewhat low. If a user wishes to effect the focus adjustment and then the diopter adjustment, he or she must move a finger away from the focus adjusting ring and set it on the diopter adjusting ring. It is likely that the diopter adjusting ring is inadvertently rotated by the finger of a typically unskilled user. He or she must move the eyes away from the ocular lens optics before the diopter adjusting ring can be visually checked. However, an object to be observed through the binoculars may be missed in the scene in the diopter adjustment. It is difficult to frame such an object in the exactly same manner even by targeting again.
Although the diopter adjustment is not required in normal use of the binoculars, it is likely that an erroneous shift of the diopter adjusting ring occurs in a manual operation of the binoculars, to require readjustment of the diopter. JP-A 2000-056205 discloses an idea for preventing errors in operating the diopter adjusting ring. Claws and grooves are used for engagement and retention in a readily releasable manner for the diopter adjusting ring. However, the retention of the diopter adjusting ring according to the document is insufficient for reliably preventing errors in the operation.